1. Field of Invention
The present invention relates to a microlens. More particularly, the present invention relates to a method of predicting the curvature radius of the microlens.
2. Description of Related Art
Microlens technology is now widely used in many optoelectronical products, for example, color digital cameras, endoscopes and color liquid crystal displays (LCD). The microlens is used to control the traveling directions of each light ray, so that the light can be precisely converged or diverged. Furthermore, through the control of digital devices, light and electricity can be interchanged digitally with each other.
For example, the converged digital camera is usually constituted by superimposing color filter arrays (CFA) either on a charge-coupled device (CCD) image sensor or on a complementary metal-oxide-semiconductor (CMOS) image sensor. In general, CFA contains three or more color filter channels arranged alternately, where each color filter channel only lets light with a specific frequency pass through, projecting to the corresponding image sensor. Therefore, the color of the image is interpreted by CFA, and then transferred to each corresponding sensor device for further processing. Furthermore, microlens arrays coupled with CFA can be used to focus the light rays, so that either the layout area of each sensor device on the substrate can be increased or the integrity can be raised.
Referring to FIG. 1, illustrating the cross-sectional view of the prior art structure containing the microlens and the sensor device, light-sensitive regions 12 are formed in a chip substrate 10. Sensor devices 14, for example, CCD or CMOS, are formed on the substrate 10. A planarized transparent layer 16 is formed on the substrate 10, with a CFA layer 18 formed thereon. Microlenses 20 are formed on the CFA layer 18, which refract light rays 22 coming from the outside to focus on the light-sensitive regions 12. Through the refraction of microlenses 20, light rays 22 are focused onto smaller areas in the light-sensitive regions 12, so that smaller areas are needed to form light-sensitive regions 12. Consequently, either the layout areas of sensor devices 14 can be increased or the integrity can be further raised.
For manufacturing the microlens in the prior art, a thermal process is usually performed to melt the patterned microlens material layer to form the microlens. In this way, it is difficult to obtain an important parameter, a curvature radius. In the past, the curvature radius was obtained by experience or by testing responses from the customers. The trial-and-error method is not only time-consuming but also imprecise.